Method of producing substantially non-oriented silicon steel strip by three-stage cold rolling

ABSTRACT

Described is a method of producing substantially non-oriented silicon steel by a three-stage cold rolling process wherein the silicon steel is temper rolled in the third or last rolling stage after normalizing to effect a reduction in gauge of about 2 to 12 percent, followed by annealing at a temperature no greater than 1,700* F for a time no longer than about 5 minutes.

United States Patent 1 Gray et al.

[ METHOD OF PRODUCING SUBSTANTIALLY NON-ORIENTED SILICON STEEL STRIP BYTHREE-STAGE COLD ROLLING [75] Inventors: Thomas 11. Gray, Pittsburgh;Jack P.

Martin, Lower Burrell, both of Pa.

[73] Assignee: Allegheny Ludlum Industries, Inc.,

' Pittsburgh, Pa.

22 Filed: Mar. 6, 1972 21 Appl. No.2 232,212

Related U.S. Application Data [63] Continuation-in-part of Ser. No.68,790, Sept. 1,

1970, abandoned.

l48/3l.55 [51] Int. Cl; H011 H04 [58] Field of Search 148/111, 110, 112,

l48/3l.55,120,12l

[ Nov. 6, 1973 Primary Examiner-L. Dewayne Rutledge Assistant ExaminerW.R. Satterfield Attorney-Vincent G. Gioia et al.

[57] ABSTRACT Described is a method of producing substantiallynonoriented silicon steel by a three-stage cold rolling process whereinthe silicon steel is temper rolled in the third or last rolling stageafter normalizing to effect a reduction in gauge of about 2 to 12percent, followed by annealing at a temperature no greater than l,700 Ffor a time no longer than about 5 minutes.

5 Claims, No Drawings METHOD OF PRODUCING SUBSTANTIALLY NON-ORIENTEDSILICON STEEL STRIP BY THREE-STAGE'COLD ROLLING CROSS REFERENCES TORELATED APPLICATIONS This application is a continuation-in-part of nowabandoned copendingapplication Ser. No. 68,790 filed Sept. 1, 1970 andassigned to the assignee of the present application.

BACKGROUND OF THE INVENTION maximum core loss for A.I.S.l. M-19transformer grade i s'l .64 watts per pound at KB. Semi-processed (i.e.,unannealed material) has a maximum core loss requirement for A.I.SLI.M-l9 grade'of 1.68 watts per pound at 15 KB. I

SUMMARY OF THE INVENTION Thepresent invention provides a method forproducing substantially non-oriented silicon steel, which complies withthe A.I.S.I. M-l9 requirements, from relatively high silicon steels suchas the following:

General Range Element Typical 2.90-3.40 Silicon 3.15 Traces 0.06 Carbon0.028 0.03-0.10 Manganese 0.065 Up to 0.03 Sulfur 0.020 Upto 0.020Phosphorus 0.008 0.05 max. Aluminum 0.0l 0030-090 Copper 0.080 Up to 0.2Nickel 0.050

Among the advantages of utilizing high silicon material in theproduction of non-oriented silicon steel is the ability to employ asingle melting and production prac tice while avoiding the need tomanufacture multiple compositions for different purposes. That is, thehigh silicon steel can be used for both the non-oriented and orientedtypes. Another advantage is that the process of the invention permitsthe use of excess quantities of high silicon material which may beproduced in the mill and which, by practicing the invention, can bediverted to the production of non-oriented products.

Previous attempts to produce non-oriented products by using high siliconsteels have generally been unsatisfactory because of the necessity forutilizing high temperature annealing treatments to develop properties.Such requirements impose undue burdens on fabricators in terms ofequipment needs and cost.

DESCRIPTION OF PREFERRED EMBODIMENT ln carrying out the invention,silicon steel containing 2.90 to 3.40 percent by weight of silicon istemper rolled in a normalized condition to effect a controlledreduction. Following temper rolling, the steel is then stress reliefannealed, preferably at a temperature less than l,700 F. A typicalprocess for producing the normalized steel of the invention is asfollows:

1. Heat ingot for a minimum of 5 hours at a temperature over 2,300 F,including 3 hours at not less than 2,400 P.

2. Roll on blooming mill to produce a slab having a thickness of 5 to 8inches and a temperature not less than 2,250" F.

3. Reduce the slab to a thickness of three-fourths to 1% inches andmaintain at a temperature not less than 2,000 F. Such reduction is at afast rate and preferably accomplished in three passes on a single strandreversing mill.

4. Admit the reduced slab at a temperature not less than 2,000 F to thefirst stand of a six-stand finishing mill and effect a reduction in thestrip to a thickness of about 0.060 to 0.10 inch at a speed to insure atemperature not less than 1,600 F at the front and back end of thestrip.

5. Descale the hot rolled strip.

6. Where desired, box or open anneal the hot rolled strip at atemperature between l,400and 2,000 F, followed by a descaling treatment.7

7. Cold roll the annealed strip in a first cold rolling step to athickness of about 1.3 to 2.5 times the final thickness.

8. Open anneal the cold rolled strip at a temperature between l,600andl,850 F.

9. Cold roll in a second cold rolling step to a thickness approximately2 to l2percent greater than the desired final thickness.

10. Open anneal the cold rolled strip to normalize the same, preferablyin a decarburizing atmosphere as in a wet reducing gas at a temperaturesubstantially between 1,400 and l,550 F.

ll. Temper roll the normalized product to effect a reduction of about 2to 12 percent.

12. Stress relief anneal at a temperature less than 1,700 Fin anon-oxidizing atmosphere for up to about 5 minutes at temperature.

As can be seen, the process of the invention involves a three-stage coldrolling process wherein the last cold rolling step comprises temperrolling and wherein the strip is normalized between the second rollingstep and the temper rolling step. Temper rolling to effect a reductionof about 2'to 12 percent has been found to be necessary to adequatelydestroy the potential for secondary recrystallization while controllingthe tendency for recrystallization to occur at lower temperatures. Thatis to say, it has been found that at least about a 2 percent reductionin the temper rolling step, and preferably about at least a 4 percentreduction, is desirable to produce material of minimum directionality.On the other hand, if the steel is unduly worked due to a reduction intemper rolling greater than about 12 percent, the minimum temperaturefor primary recrystallization is reduced and it will be difficult toobtain a coarsened primary recrystallized structure of the type desiredfor the intended applications.

The stress relief anneal, set forth in step 12 above, is preferablycarried out at less than l,700 F in a nonoxidizing atmosphere such ashydrogen or a nitrogenhydrogen mixture for up to about 5 minutes attemperature. At these low annealing temperatures, however, little sulfuris removed. When low sulfur products are desired, therefore, a lowsulfur material (e.g., less than 0.0! percent) should be used.

The following examples illustrate various embodiments of the invention:

Example No. 1

Steel having ladle chemistry shown in Table I was processed as normaloriented silicon steel strip would through final normalizing, whereuponit was temper rolled 8 percent -giving gages as shown in Table I1 andannealed at 1,500 F in pure, dry hydrogen for 15 minutes in hot zone ofmesh belt furnace 4 minutes at temperature). Properties obtained onEpstein packs of strips 1.5 X 15.25 cm. are also given in Table ll. Al1results are of 60 cycle tests.

Example No. 2

Steel of the same ladle chemistry of Example No. 1, was processed in thesame manner except for being given a 7 percent temper roll to gage shownin Table 111 followed by a 1,600 F anneal in pure dry hydrogen.Properties of the steel are also shown in that table.

TABLE 111 High Loss Low Loss End of Coil End of Coil All LongitudinalWPP at 15 KB 1.31 1.17 All Transverse WPP at 15 KB 1.78 1.89 A Long. ATrans. WPP at 15 KB 1.53 1.48 Final Gage of Sample .0125" .0123" ExampleN0. 3

Steel having the ladle chemistry given in Table IV was processed asnormal oriented silicon steel strip until after final normalizingwhereupon the sample was rolled 7 percent to gage shown, then annealedat 1,600 F in an 80 percent nitrogen 20 percent hydrogen atmosphere forthe same time as Examples 1 and 2. Properties on Epstein samples areshown in Table V.

TABLE IV C Mn P S Si Cr Ni Al Cu Sn TABLE V High Loss Low Loss End ofCoil End of Coil All Longitudinal WPP at 15 KB 1.46 1.42 All TransverseWPP at 15 KB 1.95 2.03 A Long. 5% Trans. WPP at 15 KB 1.65 1.64 FinalGage of Sample .0125" .0124" It is apparent from the foregoing examplesthat all of the materials processed in accordance with the teachings ofthe invention have a core loss below 1.64 watts per pound at 15 KB, themaximum core loss for an A.I.S.l. M-19 transformer grade.

Although the invention has been described in connection with certainspecific embodiments, it will be readily apparent to those skilled inthe art that various changes in method steps and composition can be madeto suit requirements without departing from the spirit and scope of theinvention.

We claim: l. A method of producing substantially non-oriente siliconsteel strip exhibiting a core loss below 1.64 watts per pound at 15 KB,and consisting essentially in percent by weight of 2.9 to 3.4 percentsilicon, traces to 0.06 percent carbon, 0.03 to 0.1 percent manganese,up to 0.03 percent sulfur, up to 0.02 percent phosphorus, 0.03 to 0.9percent copper, up to 0.2 percent nickel, and the balance essentiallyiron, which comprises the steps of:

heating an ingot of silicon steel at a temperature in excess of 2,300 F,

hot rolling said steel,

descaling the hot rolled steel,

cold rolling the hot rolled steel in a first cold rolling process to athickness of 1.3 to 2.5 times the final thickness of the product,

annealing the cold rolled strip at a temperature between l,600 and l,850F,

cold rolling the annealed cold rolled strip in a second cold rollingoperation to a thickness which exceeds the final thickness of theproduct by about 2to 12 percent, normalizing the cold rolled steel afterthe second cold rolling operation at a temperature between 1,400 and1,550 F,

temper rolling the normalized steel to effect a reduction of about 2 to12 percent to achieve the final thickness of the product, and

stress relief annealing the temper rolled steel at a temperature nogreater than 1,700 F and for a time period no greater than 5 minutes.

2. The method of claim 11 wherein said steel is temper rolled to effecta 4 to 12 percent reduction.

3. The method of claim 11 wherein said steel is stress relief annealedin a non-oxidizing atmosphere.

4. The method of claim 3 wherein said steel is stressrelief annealed ina hydrogen-containing atmosphere.

5. The method of claim 1 wherein said steel has less than 0.01 percentsulfur.

2. The method of claim 1 wherein said steel is temper rolled to effect a4 to 12 percent reduction.
 3. The method of claim 1 wherein said steelis stress relief annealed in a non-oxidizing atmosphere.
 4. The methodof claim 3 wherein said steel is stress-relief annealed in ahydrogen-containing atmosphere.
 5. The method of claim 1 wherein saidsteel has less than 0.01 percent sulfur.